The present invention relates to a bearing assembly and in particular to a spherical bearing assembly.
FIG. 1 illustrates a known type of spherical bearing 1 comprising a housing 2 and a ball 3 partially housed within the housing 2. The housing 2 comprises a race 4 having a spherical bearing surface 7, a sleeve 5 surrounding the race 4, and an elastomer 6 disposed between and bonded to the race 4 and sleeve 5. The race 4 and sleeve 5 are arranged coaxially about a central axis of the housing 2. The ball 3 is mounted within the race 4 such that the ball 3 is free to rotate but is prevented from any significant translational movement within the race 4.
The elastomer 6 serves to absorb displacement of the ball 3 relative to the housing 2 in a radial direction, i.e. in a direction normal to the central axis of the housing 2. As a result, the bearing assembly 1 is able to dampen radial vibrations as well as compensate for minor misalignments in the objects to which the bearing assembly 1 is mounted.
A problem with the bearing assembly 1 of FIG. 1 is that it is ill-equipped at accommodating forces which act on the ball 3 in a direction parallel to the central axis of the housing 2, referred to hereafter as axial forces. Axial forces acting on the ball 3 cause the ball 3 to be displaced axially relative to the housing 2, i.e. in a direction parallel to the central axis. Owing to the engagement of the race 4 with the ball 3, axial displacement of the ball 3 causes the race 4 to be displaced in the same direction. This displacement of the race 4 relative to the sleeve 5 creates shearing forces between the race 4 and sleeve 5. Consequently, repeated or excessive axial displacement of the race 4 relative to the sleeve 5 can lead to one or both of the race:elastomer and sleeve:elastomer interfaces shearing with the subsequent separation of the elastomer 6 from the race 4 and/or sleeve 5. When this occurs, the ball 2 and race 4 are free to separate from the sleeve 5 resulting in failure of the bearing 1.
There is a threshold torque between the ball 3 and housing 2 below which there is no resultant movement of the ball 3 relative to the housing 2. Above the threshold torque, the ball 3 is caused to rotate within the housing 2. The bearing assembly 1 of FIG. 1 is poorly-equipped at accommodating rotational forces below the threshold torque which may act on the bearing assembly 1, i.e. forces which cause the ball 3 to rotate within the housing 2. Owing to frictional forces which act between the ball 3 and race 4, rotation of the ball 3 within the race 4 encourages the race 4 to similarly rotate. This is particularly true when the bearing 1 is secured to a body by interference fit, which results in the housing 2 being radially compressed. Any rotation of the race 4 relative to the sleeve 5 will again create shearing forces. Consequently, although the bearing 1 is designed to facilitate rotation of the ball 3 within the housing 2, the bearing 1 is susceptible to failure with repeated rotation of the ball 3 below the threshold torque, due to shearing of the race:elastomer and/or sleeve:elastomer interfaces.
The present invention provides a bearing assembly that overcomes one or more of the aforementioned disadvantages of the aforementioned design by more effectively accommodating axial and/or rotational forces.